The present invention relates to ablator compositions for protecting the underlying structure of a spacecraft or the like from the aerodynamic heating caused by travel at high speed during reentry through the atmosphere. An ablating material which is to be applied to the exterior of the underlying structure is prepared by curing the ablator composition.
As thermal protection materials for the underlying structure of a spacecraft or the like, for example, carbon/carbon-fiber composite materials, high melting point oxides, nitrides and carbides are known.
It is mentioned in Revised Handbook of Aeronautics and Astronautics (written in Japanese, published on Apr. 25, 1983, p. 242) that ablation cooling by latent heat through volatilization (sublimation) of a solid into a gas may be also taken as one of the thermal protections.
JP-A-58-161985 discloses a low density ablator composition comprising a mixture of a silicone resin and silica microballoons wherein the silica microballoons contain at least 85.0 wt. % of SiO.sub.2 and the weight ratio of the silica microballoons to the silicone resin is in a range of from 50:50 to 70:30.
U.S. Pat. No. 4,031,059 discloses a low density ablator composition which has a density of not greater than 0.25 g/cc and comprises a polysiloxane, a low density filler, hollow silica or glass microspheres, and silica fibers.
Conventional ablating materials such as those of the above patent publications are satisfactory in thermal protection under a condition of a low heating rate ranging from about 0.5 to about 1.0 MW/m.sup.2 and a low pressure of about 0.1 atmospheric pressure.
Recently, a demand for ablating materials which are satisfactory in thermal protection even under a condition of a high heating rate such as about 4 MW/m.sup.2 and a high pressure such as about one atmospheric pressure has been increased. Furthermore, a demand for ablating materials which can prevent damage caused by thermal shock and are superior in brittleness at a low temperature has been increased.